This application is a national stage application filed under 35 U.S.C. 371 of International Patent Appln. No. PCT/GB98/01294, filed May 5, 1998.
This invention relates particularly to gene directed enzyme prodrug therapy (GDEPT) using in situ antibody generation to provide enhanced selectivity, particularly for use in cancer therapy.
Known gene therapy based prodrug therapeutic approaches include virus-directed enzyme prodrug therapy (VDEPT) and gene-directed enzyme prodrug therapy (GDEPT), the latter term encompassing both VDEPT and non-viral delivery systems. VDEPT involves targeting tumour cells with a viral vector carrying a gene which codes for an enzyme capable of activating a prodrug. The viral vector enters the tumour cell and enzyme is expressed from the enzyme gene inside the cell. In GDEPT, alternative approaches such as microinjection, liposomal delivery and receptor mediated DNA uptake as well as viruses may be used to deliver the gene encoding the enzyme.
In both VDEPT and GDEPT the enzyme gene can be transcriptionally regulated by DNA sequences capable of being selectively activated in mammalian cells e.g. tumour cells (EP 415 731 (Wellcome); Huber et al, Proc. Natl. Acad. Sci. USA. 88, 8039-8043, 1991). While giving some degree of selectivity, gene expression may also occur in non-target cells and this is clearly undesirable when the approach is being used to activate prodrugs into potent cytotoxic agents. In addition these regulatory sequences will generally lead to reduced expression of the enzyme compared with using viral promoters and this will lead to a reduced ability to convert prodrug in the target tissue.
Expression and localisation of the prodrug activating enzyme inside the cell has disadvantages. Prodrug design is severely limited by the fact that the prodrug has to be able to cross the cell membrane and enter the cell but not be toxic until it is converted to the drug inside the cell by the activating enzyme. Most prodrugs utilise hydrophilic groups to prevent cell entry and thus reduce cytotoxicity. Prodrug turnover by activating enzyme produces a less hydrophilic drug which can enter cells to produce anti-cancer effects. This approach can not be used when the activating enzyme is expressed inside the cell. Another disadvantage is that target cells which lack intracellular activating enzyme will be difficult to attack because they are unable to generate active drug. To achieve this desirable xe2x80x9cbystander activityxe2x80x9d (or xe2x80x9cneighbouring cell killxe2x80x9d), the active drug will have to be capable of diffusion out of the cell containing activating enzyme to reach target cells which lack enzyme expression. Many active drugs when produced inside a cell will be unable to escape from the cell to achieve this bystander effect.
Modifications of GDEPT have been put forward to overcome some of the problems described above. Firstly vectors have been described which are said to express the activating enzyme on the surface of the target cell (WO 96/03515) by attaching a signal peptide and transmembrane domain to the activating enzyme. The approach, if viable, would overcome the problems of having the activating enzyme located inside the cell but would still have to rely on transcriptionally regulated sequences capable of being selectively expressed in target cells to restrict cell expression. As described above there are disadvantages of using such sequences. Secondly vectors have been described which result in secretion of the enzyme from the target cell (WO 96/16179). In this approach the enzyme would be able to diffuse away from its site of generation since it is extracellular and not attached to the cell surface. Enzyme which has diffused away from the target site would be capable of activating prodrug at non-target sites leading to unwanted toxicity. To achieve some selectivity it is suggested that enzyme precursors could be used which are cleaved by pathology associated proteases to form active enzyme. Some selectivity is likely to be achieved by this approach but its unlikely that activation will only occur at target sites. In addition, once activated, the enzyme will still be free to diffuse away from the target site and thus suffer from the same drawback described above.
For GDEPT approaches, three levels of selectivity can be observed. Firstly, there is selectivity at the cell infection stage such that only specific cell types are targeted. For example cell selectivity can be provided by the gene delivery system per se. An example of this type of selectivity is set out in International Patent Application WO 95/26412 (UAB Research Foundation) which describes the use of modified adenovirus fiber proteins incorporating cell specific ligands. Other examples of cell specific targeting include ex vivo gene transfer to specific cell populations such as lymphocytes and direct injection of DNA into muscle tissue.
The second level of selectivity is control of gene expression after cell infection such as for example by the use of cell or tissue specific promoters. If the gene has been delivered to a cell type in a selective manner then it is important that a promoter is chosen that is compatible with activity in the cell type.
The third level of selectivity can be considered as the selectivity of the expressed gene construct. Selectivity at this level has received scant attention to date. In International patent application WO 96/16179 (Wellcome Foundation) it is suggested that enzyme precursors could be used which are cleaved by pathology associated proteases to form active enzyme. Some selectivity is likely to be achieved by this approach but it is unlikely that activation will only occur at target sites. In addition, once activated, the enzyme will still be free to diffuse away from the target site and thus suffer from the same drawback of activating prodrug at non-target sites leading to unwanted toxicity.
There exists a need for more selective GDEPT systems to reduce undesirable effects in normal tissues arising from erroneous prodrug activation.
The present invention is based on the discovery that antibody-heterologous enzyme gene constructs can be expressed intracellularly and used in GDEPT systems (or other systems such as AMIRACSxe2x80x94see below) for cell targeting arising from antibody specificity to deliver cell surface available enzyme in a selective manner. This approach may be used optionally in combination with any other suitable specificity enhancing technique(s) such as targeted cell infection and/or tissue specific expression.
According to one aspect of the present invention there is provided a gene construct encoding a cell targeting antibody and a heterologous enzyme for use as a medicament in a mammalian host wherein the gene construct is capable of expressing the antibody and enzyme as a conjugate within a target cell in the mammalian host and wherein the conjugate can leave the cell thereafter for selective localisation at a cell surface antigen recognised by the antibody.
According to another aspect of the present invention there is provided a gene construct encoding a cell targeting moiety and a heterologous prodrug activating enzyme for use as a medicament in a mammalian host wherein the gene construct is capable of expressing the cell targeting moiety and heterologous prodrug activating enzyme as a conjugate within a cell in the mammalian host and wherein the conjugate is directed to leave the cell thereafter for selective localisation at a cell surface antigen recognised by the cell targeting moiety.
The xe2x80x9ccell targeting moietyxe2x80x9d is defined as any polypeptide or fragment thereof which selectively binds to a particular cell type in a host through recognition of a cell surface antigen. Preferably the cell targeting moiety is an antibody. Cell targeting moieties other than antibodies include ligands as described for use in Ligand Directed Enzyme Prodrug Therapy as described in International patent application WO 97/26918, Cancer Research Campaign Technology Limited, such as for example epidermal growth factor, heregulin, c-erbB2 and vascular endothelial growth factor with the latter being preferred.
A xe2x80x9ccell targeting antibodyxe2x80x9d is defined as an antibody or fragment thereof which selectively binds to a particular cell type in a host through recognition of a cell surface antigen. Preferred cell targeting antibodies are specific for solid tumours, more preferably colorectal tumours, more preferably an anti-CEA antibody, more preferably antibody A5B7 or 806.077 antibody with 806.077 antibody being especially preferred. Hybridoma 806.077 antibody was deposited at the European Collection of Animal Cell Cultures (ECACC), PHLS Centre for Applied Microbiology and Research, Porton Down, Salisbury, Wiltshire SP4 0JG, United Kingdom on Feb. 29, 1996 under accession no. 96022936 in accordance with the Budapest Treaty.
Antibody A5B7 binds to human carcinoembryonic antigen (CEA) and is particularly suitable for targeting colorectal carcinoma. A5B7 is available from DAKO Ltd., 16 Manor Courtyard, Hughenden Avenue, High Wycombe, Bucks HP13 5RE, England, United Kingdom. In general the antibody (or antibody fragment)xe2x80x94enzyme conjugate should be at least divalent, that is to say capable of binding to at least 2 tumour associated antigens (which may be the same or different). Antibody molecules may be humanised by known methods such as for example by xe2x80x9cCDR graftingxe2x80x9d as disclosed in EP239400 or by grafting complete variable regions from for example a murine antibody onto human constant regions (xe2x80x9cchimaeric antibodiesxe2x80x9d) as disclosed in U.S. Pat. No. 4,816,567. Humanised antibodies may be useful for reducing immunogenicity of an antibody (or antibody fragment). A humanised version of antibody A5B7 has been disclosed in International Patent Application WO 92/01059 (Celltech).
The hybridoma which produces monoclonal antibody A5B7 was deposited with the European Collection of Animal Cell Cultures, Division of Biologics, PHLS Centre for Applied Microbiology and Research, Porton Down, Salisbury, Wiltshire SP4 0JG, United Kingdom. The date of deposit was Jul. 14, 1993 and the accession number is No. 93071411. Antibody A5B7 may be obtained from the deposited hybridoma using standard techniques known in the art such as documented in Fenge C, Fraune E and Schuegerl K in xe2x80x9cProduction of Biologicals from Animal Cells in Culturexe2x80x9d (Spier R E, Griffiths J R and Meignier B, eds) Butterworth-Heinemann, 1991, 262-265 and Anderson B L and Gruenberg M L in xe2x80x9cCommercial Production of Monoclonal Antibodiesxe2x80x9d (Seaver S, ed), Marcel Dekker, 1987, 175-195. The cells may require re-cloning from time to time by limiting dilution in order to maintain good levels of antibody production.
A xe2x80x9cheterologous enzymexe2x80x9d is defined as an enzyme for turning over a substrate that has been administered to the host and the enzyme is not naturally present in the relevant compartment of the host. The enzyme may be foreign to the mammalian host (e.g. a bacterial enzyme like CPG2) or it may not naturally occur within the relevant host compartment (e.g. the use of lysozyme as an ADEPT enzyme (for an explanation of ADEPT see below) is possible because lysozyme does not occur naturally in the circulation, see U.S. Pat. No. 5,433,955, Akzo Nev.). The relevant host compartment is that part of the mammalian host in which the substrate is distributed. Preferred enzymes are enzymes suitable for ADEPT or AMIRACS (Antimetabolite with Inactivation of Rescue Agents at Cancer Sites; see Bagshawe (1994) in Cell Biophysics 24/25, 83-91) but ADEPT enzymes are preferred. Antibody directed enzyme prodrug therapy (ADEPT) is a known cancer therapeutic approach. ADEPT uses a tumour selective antibody conjugated to an enzyme. The conjugate is administered to the patient (usually intravenously), allowed to localise at the tumour site(s) and clear from the blood and other normal tissues. A prodrug is then administered to the patient which is converted by the enzyme (localised at the tumour site) into a cytotoxic drug which kills the tumour cells.
In International Patent Application WO 96/20011, published Jul. 4, 1996, we proposed a xe2x80x9creversed polarityxe2x80x9d ADEPT system based on mutant human enzymes having the advantage of low immnunogenicity compared with for example bacterial enzymes. A particular host enzyme was human pancreatic CPB (see for example, Example 15 [D253K]human CPB and 16 [D253R]human CPB therein) and prodrugs therefor (see Examples 18 and 19 therein). The host enzyme is mutated to give a change in mode of interaction between enzyme and prodrug in terms of recognition of substrate compared with the native host enzyme. In our subsequent International Patent Application No PCT/GB96/01975 (published Mar. 6, 1997 as WO 97/07796) further work on mutant CPB enzyme/prodrug combinations for ADEPT are described. Preferred enzymes suitable for ADEPT are any one of CPG2 or a reversed polarity CPB enzyme, for example any one of [D253K]HCPB, [G251T,D253K]HCPB or [A248S,G251T,D253K]HCPB. A preferred form of CPG2 is one in which the polypeptide glycosylation sites have been mutated so as to prevent or reduce glycosylation on expression in mammalian cells (see WO 96/03515, Cancer Research Campaign Technology); this gives improved enzyme activity. Further considerations arise for enzymes such as CPB which require a pro domain to facilitate correct folding; here the pro domain can either be expressed as a separately (in trans) or expressed as part of the fusion protein and subsequently removed.
Large scale purification of CPG2 from Pseudomonas RS-16 was described in Sherwood et al (1985), Eur, J. Biochem., 148, 447-453. CPG2 may be obtained from Centre for Applied Microbiology and Research, Porton Down, Salisbury, Wiltshire SP4 0JG, United Kingdom. CPG2 may also be obtained by recombinant techniques. The nucleotide coding sequence for CPG2 has been published by Minton, N. P. et al., Gene, 31 (1984), 31-38. Expression of the coding sequence has been reported in E.coli (Chambers, S. P. et al., Appl. Microbiol, Biotechnol. (1988), 29, 572-578) and in Saccharomyces cerevisiae (Clarke, L. E. et al., J. Gen Microbiol, (1985) 131, 897-904). Total gene synthesis has been described by M. Edwards in Am. Biotech. Lab (1987), 5, 38-44. Expression of heterologous proteins in E.coli has been reviewed by F. A. O. Marston in DNA Cloning Vol. III, Practical Approach Series, IRL Press (Editor D M Glover), 1987, 59-88. Expression of proteins in yeast has been reviewed in Methods in Enzymology Volume 194, Academic Press 1991, Edited by C. Guthrie and G R Fink.
Whilst cancer therapeutic approaches are preferred the invention may also be applied to other therapeutic areas as long as a target antigen can be selected and a suitable enzyme/prodrug combination prepared. For example, inflammatory diseases such as rheumatiod arthritis may be treated by for example using an antibody selective for synovial cells fused to an enzyme capable of converting an anti-inflammatory drug in the form of a prodrug into an anti-inflammatory drug. Use of antibodies to target rheumatoid arthritis disease has been described in Blakey et al, 1988, Scand. J. Rheumatology, Suppl. 76, 279-287.
A xe2x80x9cconjugatexe2x80x9d between antibody and enzyme can be a fusion protein (covalent linkage) or the conjugate can be formed by non-covalent binding between antibody and enzyme formed in situ. Preferably the conjugate is in the form of a fusion protein, more preferably the antibody component of the fusion is at least divalent (for improved binding avidity compared with monovalent antibody). Antibody constructs lacking an Fc portion are preferred, especially Fab or F(abxe2x80x2)2 fragments. For CPG2 fusions (or fusions with any non-monomeric enzyme) special considerations apply because CPG2 is a dimeric enzyme and the antibody is preferably divalent thus there exists the potential for undesirable competing dimerisation between two molecular species. Therefore a preferred CPG2 fusion is one in which the fusion protein is formed through linking a C-terminus of an antibody Fab heavy chain (ie lacking a hinge region) to an N-terminus of a CPG2 molecule; two of these Fab-CPG2 molecules then dimerise through the CPG2 dimerisation domain to form a (Fab-CPG2)2 conjugate. For antibody constructs with monomeric enzymes, F(abxe2x80x2)2 fragments are preferred, especially F(abxe2x80x2)2 fragments having a human IgG3 hinge region. Fusions between antibody and enzyme may optionally be effected through a short peptide linker such as for example (G4S)3. Preferred fusion constructs are those in which the enzyme is fused to the C terminus of the antibody, through the heavy or light chain thereof with fusion through the antibody heavy chain being preferred. Accordingly a preferred gene construct is a gene construct for use as a medicament as described herein in which the antibody-enzyme CPG2 conjugate is a fusion protein in which the enzyme is fused to the C terminus of the antibody through the heavy or light chain thereof whereby dimerisation of the encoded conjugate when expressed can take place through a dimerisation domain on CPG2. A more preferred gene construct is a gene construct for use as a medicament wherein the fusion protein is formed through linking a C-terminus of an antibody Fab heavy chain to an N-terminus of a CPG2 molecule to form a Fab-CPG2 whereby two Fab-CPG2 molecules when expressed dimerise through CPG2 to form a (Fab-CPG2)2 conjugate. In another embodiment of the invention a preferred gene construct for use as a medicament is one wherein the carboxypeptidase is selected from [D253K]HCPB, [G251T,D253K]HCPB or [A248S,G251T,D253K]HCPB.
It is contemplated that should it be possible to obtain a natural multimeric enzyme in monomeric form whilst substantially retaining enzymic activity then the monomeric form of the enzyme could be used to form a conjugate of the invention. Similarly, it is contemplated that should it be possible to obtain a natural monomeric enzyme in multimeric form whilst substantially retaining enzymic activity then the multimeric form of the enzyme could be used to form a conjugate of the invention.
The conjugate is directed to leave the cell after expression therein through use of a secretory leader sequence which is cleaved as the conjugate passes through the cell membrane. Preferably the secretory leader is the secretory leader that occurs naturally with the antibody.
According to another aspect of the present invention there is provided use of a gene construct encoding a cell targeting antibody and a heterologous enzyme for use for manufacture of a medicament for cancer therapy in a mammalian host wherein the gene construct is capable of expressing the antibody and enzyme as a conjugate within a target cell in the mammalian host and wherein the conjugate can leave the cell thereafter for selective localisation at a cell surface antigen recognised by the antibody.
Any suitable delivery system may be applied to deliver the gene construct of the present invention including viral and non-viral systems. Viral systems include retroviral vectors, adenoviral vectors, adeno-associated virus, vaccinia, herpes simplex virus, HIV, the minute virus of mice, hepatitis B virus and influenza virus. Non-viral systems include uncomplexed DNA, DNA-liposome complexes, DNA-protein complexes and DNA-coated gold particles.
Retroviral vectors lack immunogenic proteins and there is no preexisting host immunity but are limited to infecting dividing cells. Retroviruses have been used in clinical trials (Rosenberg et al., N. Engl. J. Med., 1990, 323: 570-578). Retroviruses are composed of an RNA genome that is packaged in an envelope derived from host cell membrane and viral proteins. For gene expression, it must first reverse transcribe its positive-strand RNA genome into double-stranded DNA, which is then integrated into the host cell DNA using reverse transcriptase and integrase protein contained in the retrovirus particle. The integrated provirus is able to use host cell machinery for gene expression.
Murine leukemia virus is widely used (Miller et al., Methods Enzymol., 1993, 217: 581-599). Retroviral vectors are constructed by removal of the gag, pol and env genes to make room for the relevant payload and to eliminate the replicative functions of the virus. Virally encoded mRNAs are eliminated and this removes any potential immune response to the transduced cells. Genes encoding antibiotic resistance often are included as a means of selection. Promoter and enhancer functions also may be included for example to provide for tissue-specific expression after administration in vivo. Promoter and enhancer functions contained in the long terminal repeat may also be used.
These viruses can be produced only in viral packaging cell lines. The packaging cell line may be constructed by stably inserting the deleted viral genes (gag, pol. and env) into the cell such that they reside on different chromosomes to prevent recombination. The packaging cell line is used to construct a producer cell line that will generate replication-defective retrovirus containing the relevant payload gene by inserting the recombinant proviral DNA. Plasmid DNA containing the long terminal repeat sequences flanking a small portion of the gag gene that contains the encapsidation sequence and the genes of interest is transfected into the packaging cell line using standard techniques for DNA transfer and uptake (electroporation, calcium precipitation, etc.). Variants of this approach have been employed to decrease the likelihood of production of replication-competent virus (Jolly, D., Cancer Gene Therapy, 1994, 1, 51-64). The host cell range of the virus is determined by the envelope gene (env) and substitution of env genes with different cell specificities can be employed. Incorporation of appropriate ligands into the envelope protein may also be used for targeting.
Administration may be achieved by any suitable technique e.g. ex vivo transduction of patients"" cells, by the direct injection of virus into tissue, and by the administration of the retroviral producer cells.
The ex vivo approach has a disadvantage in that it requires the isolation and maintenance in tissue culture of the patient""s cells, but it has the advantage that the extent of gene transfer can be quantified readily and a specific population of cells can be targeted. In addition, a high ratio of viral particles to target cells can be achieved and thus improve the transduction efficiency (Anderson et al., Hum. Gene Ther., 1990, 1: 331-341; Rosenberg et al., N. Engl. J. Med., 1990, 323: 570-578; Culver et al., Hum. Gene Ther., 1991, 2: 107-109 Nienhuis et al., Cancer, 1991, 67: 2700-2704, Anderson et al., Hum. Gene Ther., 1990, 1: 331-341, Grossman et al., Nat. Genet., 1994, 6:335-341, Lotze el al., Hum. Gene Ther., 1992, 3: 167-177; Lotze, M. T., Cell Transplant., 1993, 2: 33-47; Lotze et al., Hum. Gene Ther., 1994, 5: 41-55 and U.S. Pat. No. 5,399,346 (Anderson). In some cases direct introduction of virus in vivo is necessary. Retroviruses have been used to treat brain tumours wherein the ability of a retrovirus to infect only dividing cells (tumour cells) may be particularly advantageous.
To increase efficiency Oldfield et al., in Hum. Gene Ther., 1993, 4: 39-69 proposed the administration of a retrovirus producer cell line directly into patients"" brain tumours. The murine producer cell would survive within the brain tumour for a period of days, and would secrete retrovirus capable of transducing the surrounding brain tumour. Virus carrying the herpes virus thymidine kinase gene renders cells susceptible to killing by ganciclovir, which is metabolized to a cytotoxic compound by thymidine kinase. Patent references on retroviruses are: EP 334301, WO 91/02805 and WO 92/05266 (Viagene) and; U.S. Pat. No. 4,650,764 (University of Wisconsin).
Human adenoviral infections have been described (see Horwitz, M. S., In Virology, 2nd ed. Raven Press, New York, 1990, pp. 1723-1740). Most adults have prior exposure to adenovirus and have antiadenovirus antibodies. These viruses possess a double-stranded DNA genome, and replicate independent of host cell division.
Adenoviral vectors possess advantageous properties. They are capable of transducing a broad spectrum of human tissues and high levels of gene expression can be obtained in dividing and nondividing cells. Several routes of administration can be used including intravenous, intrabiliary, intraperitoneal, intravesicular, intracranial and intrathecal injection, and direct injection of the target organ. Thus targeting based on anatomical boundaries is feasible.
The adenoviral genome encodes about 15 proteins and infection involves a fiber protein to bind a cell surface receptor. The penton base of the capsid engages integrin receptor domains (xcex13xcex23, or xcex13xcex25) on the cell surface resulting in internalization of the virus. Viral DNA enters the nucleus and begins transcription without cell division. Expression and replication is under control by the E1A and E1B genes (see Horwitz, M. S., In Virology, 2nd ed., 1990, pp. 1723-1740). Removal of E1 genes renders the virus replication-incompetent. Expression of adenoviral proteins leads to both an immune response which may limit effectiveness particularly on repeat administration. However, recent approaches in which other adenoviral genes such as the E2a gene (which controls expression of the fibre knob and a number of other viral proteins) are also removed from the viral genome may abolish or greatly reduce the expression of many of these viral proteins in target cells.
Adenoviral serotypes 2 and 5 have been extensively used for vector construction. Bett et al., Proc. Nat. Acad. Sci. U.S.A., 1994, 91: 8802-8806 have used an adenoviral type 5 vector system with deletions of the E1 and E3 adenoviral genes. The 293 human embryonic kidney cell line has been engineered to express E1 proteins and can thus transcomplement the E1-deficient viral genome. The virus can be isolated from 293 cell media and purified by limited dilution plaque assays (Graham, F. L. and Prevek, L. In Methods in Molecular Biology: Gene Transfer and Expression Protocols, Humana Press 1991, pp. 109-128). Recombinant virus can be grown in 293 cell line cultures and isolated by lysing infected cells and purification by caesium chloride density centrifugation. One problem of the 293 cells for manufacture of recombinant adenovirus is that due to additional flanking regions of the E1 genes is that they may give rise to replication competent adenovirus (RCA) during the viral particle production. Although this material is only wild type adenovirus and not replication competent recombinant virus it can have significant effects on the eventual yield of the desired adenoviral material and lead to increased manufacturing costs, quality control issues for the production runs and acceptance of batches for clinical use. Alternative cell lines such as the PER.C6 which have more defined E1 gene integration than 293 cells (i.e. contain not flanking viral sequence) have been developed which do not allow the recombination events which produce RCA and thus have the potential to overcome above viral production issues.
Adenoviral vectors have the disadvantage of relatively short duration of transgene expression due to immune system clearance and dilutional loss during target cell division but improvements in vector design are anticipated. Patent references on adenoviruses are: WO 96/03517 (Boehringer); WO 96/13596 (Rhone Poulenc Rorer); WO 95/29993 (University of Michigan) and; WO 96/34969 (Canji). Recent advances in adenoviral vectors for cancer gene therapy including the development of strategies to reduce immunogenicity, chimeric adenoviral/retroviral vectors and conditional (or restricted) replicative recombinant adenoviral systems are reviewed in Bilbao et al., Exp. Opin. Ther. Patents, 1997, 7 (12):1427-1446.
Adeno-associated virus (AAV) (Kotin, R. M., Hum. Gene Ther., 1994, 5: 793-801) are single-stranded DNA, nonautonomous parvoviruses able to integrate into the genome of nondividing cells of a very broad host range. AAV has not been shown to be associated with human disease and does not elicit an immune response.
AAV has two distinct life cycle phases. Wild-type virus will infect a host cell, integrate and remain latent. In the presence of adenovirus, the lytic phase of the virus is induced, which is dependent on the expression of early adenoviral genes, and leads to active virus replication. The AAV genome is composed of two open reading frames (called rep and cap) flanked by inverted terminal repeat (ITR) sequences. The rep region encodes four proteins which mediate AAV replication, viral DNA transcription, and endonuclease functions used in host genome integration. The rep genes are the only AAV sequences required for viral replication. The cap sequence encodes structural proteins that form the viral capsid. The ITRs contain the viral origins of replication, provide encapsidation signals, and participate in viral DNA integration. Recombinant, replication-defective viruses that have been developed for gene therapy lack rep and cap sequences. Replication-defective AAV can be produced by cotransfecting the separated elements necessary for AAV replication into a permissive 293 cell line. Patent references on AAV include: WO 94/13788 (University of Pittsburgh) and U.S. Pat. No. 4,797,368 (US Department of Health).
Gene therapy vectors from pox viruses have been described (Moss, B. and Flexner, C., Annu. Rev. Immunol., 1987, 5: 305-324; Moss, B., In Virology, 1990, pp. 2079-2111). Vaccinia are large, enveloped DNA viruses that replicate in the cytoplasm of infected cells. Nondividing and dividing cells from many different tissues are infected, and gene expression from a nonintegrated genome is observed. Recombinant virus can be produced by inserting the transgene into a vaccinia-derived plasmid and transfecting this DNA into vaccinia-infected cells where homologous recombination leads to the virus production. A significant disadvantage is that it elicits a host immune response to the 150 to 200 virally encoded proteins making repeated administration problematic.
The herpes simplex virus is a large, double-stranded DNA virus that replicates in the nucleus of infected cells suitable for gene delivery (see Kennedy, P. G. E. and Steiner, I., Q. J. Med., 1993, 86: 697-702). Advantages include a broad host cell range, infection of dividing and nondividing cells, and large sequences of foreign DNA can be inserted into the viral genome by homologous recombination. Disadvantages are the difficulty in rendering viral preparations free of replication-competent virus and a potent immune response. Deletion of the viral thymidine kinase gene renders the virus replication-defective in cells with low levels of thymidine kinase. Cells undergoing active cell division (e.g., tumour cells) possess sufficient thymidine kinase activity to allow replication. Cantab Pharmaceuticals have a published patent application on herpes viruses (WO 92/05263).
A variety of other viruses, including HIV, the minute virus of mice, hepatitis B virus, and influenza virus, have been considered as possible vectors for gene transfer (see Jolly, D., Cancer Gene Therapy, 1994, 1: 51-64).
The use of attenuated Salmonella Typhimurium bacteria which specifically target and replicate in hypoxic environments (such as are found in the necrotic centres of tumours) as gene delivery vehicles for prodrug enzyme based therapy (Tumour Amplified Prodrug Enzyme Therapy known as TAPET(trademark)) has also been proposed and is under development by Vion Pharmaceuticals. This system offers a further gene delivery alternative to the viral and non-viral delivery approaches discussed below.
Nonviral DNA delivery strategies are also applicable. These DNA delivery systems include uncomplexed plasmid DNA, DNA-liposome complexes, DNA-protein complexes, and DNA-coated gold particles.
Purified nucleic acid can be injected directly into tissues and results in transient gene expression for example in muscle tissue, particularly effective in regenerating muscle (Wolff et al., Science, 1990, 247: 1465-1468). Davis et al., in Hum. Gene Ther., 1993, 4: 733-740 has published on direct injection of DNA into mature muscle. Skeletal and cardiac muscle is generally preferred. Patent references are: WO 90/11092, U.S. Pat. No. 5,589,466 (Vical) and WO 97/05185 (biodegradable DNA impregnated hydrogels for injection, Focal).
Plasmid DNA on gold particles can be xe2x80x9cfiredxe2x80x9d into cells (e.g. epidermis or melanoma) using a gene-gun. DNA is coprecipitated onto the gold particle and then fired using an electric spark or pressurized gas as propellant (Fynan et al., Proc. Natl. Acad. Sci. U.S.A., 1993, 90: 11478-11482). Electroporation has also been used to enable transfer of DNA into solid tumours using electroporation probes employing multi-needle arrays and pulsed, rotating electric fields (Nishi et al., in Cancer Res., 1996, 56:1050-1055). High efficiency gene transfer to subcutaneous tumours has been claimed with significant cell transfection enhancement and better distribution characteristics over intra-tumoural injection procedures.
Liposomes work by surrounding hydrophilic molecules with hydrophobic molecules to facilitate cell entry. Liposomes are unilamellar or multilamellar spheres made from lipids. Lipid composition and manufacturing processes affect liposome structure. Other molecules can be incorporated into the lipid membranes. Liposomes can be anionic or cationic. Nicolau et al., Proc. Natl. Acad. Sci. U.S.A., 1983, 80: 1068-1072 has published on insulin expression from anionic liposomes injected into rats. Anionic liposomes mainly target the reticuloendothelial cells of the liver, unless otherwise targeted. Molecules can be incorporated into the surface of liposomes to alter their behavior, for example cell-selective delivery (Wu, G. Y. and Wu, C. H., J. Biol. Chem., 1987, 262: 4429-4432).
Felgner et al., Proc. Nat. Acad. Sci. U.S.A., 1987, 84: 7413-7417 has published on cationic liposomes, demonstrated their binding of nucleic acids by electrostatic interactions and shown cell entry. Intravenous injection of cationic liposomes leads to transgene expression in most organs on injection into the afferent blood supply to the organ. Cationic liposomes can be administered by aerosol to target lung epithelium (Brigham et al., Am. J. Med. Sci., 1989, 298: 278-281). Patent references on liposomes are: WO 90/11092, WO 91/17424, WO 91/16024, WO 93/14788 (Vical) and; WO 90/01543 (Intracel).
In-Vivo studies with cationic liposome transgene delivery have been published by: Nabel et al., Rev. Hum. Gene Ther., 1994, 5: 79-92; Hyde et al., Nature, 1993, 362: 250-255 and; Conary et al., J. Clin. Invest., 1994, 93: 1834-1840).
Microparticles are being studied as systems for delivery of DNA to phagocytic cells such approaches have been pursued by Pangaea Pharmaceuticals in their ENDOSHERE(trademark) DNA microencapsulation delivery system which has been used to effect more efficient transduction of phagocytic cells such as macrophages which ingest the microspheres. The microspheres encapsulate plasmid DNA encoding potentially immunogenic peptides which when expressed lead to peptide display via MHC molecules on the cell surface which can stimulate immune response against such peptides and protein sequences which contain the same epitopes. This approach is presently aimed towards a potential role in anti-tumour and pathogen vaccine development but may have other possible gene therapy applications.
In the same way as synthetic polymers have been used to package DNA natural viral coat proteins which are capable of homogeneous self-assembly into Virus-like particles (VLPs) have been used to package DNA. The major structural coat protein VP1 of human polyoma virus can be expressed as a recombinant protein and is able to package plasmid DNA during self-assembly into a VLP. The resulting particles can be subsequently used to transduce various cell lines, while preliminary studies show little immunogenic response to such VP1 based VLPs. Such systems may offer an attractive intermediate between synthetic polymer non-viral vectors and the alternative viral delivery systems since they may offer combined advantages e.g. simplicity of production and high level transduction efficiency.
To improve the specificity of gene delivery and expression the therapeutic gene the inclusion of targeting elements into the delivery vehicles and the use of regulatory expression elements have been investigated both singlulary and in combination in many of the previously described delivery systems.
Improvements in DNA vectors have also been made and are likely applicable to all of the non-viral delivery systems. These include the use of supercoiled minicircles reported by RPR Gencell (which do not have bacterial origins of replication nor antibiotic resistance genes and thus are potentially safer as they exhibit a high level of biological containment), episomal expression vectors as developed by Copernicus Gene Systems Inc (replicating episomal expression systems where the plasmid amplifies within the nucleus but outside the chromosome and thus avoids genome integration events) and T7 systems as developed by Progenitor (a strictly a cytoplasmic expression vector in which the vector itself expresses phage T7 RNA polymerase and the therapeutic gene is driven from a second T7 promoter, using the polymerase generated by the first promoter). Other, more general improvements to DNA vector technology include use of cis-acting elements to effect high levels of expression (Vical), sequences derived from alphoid repeat DNA to supply once-per-cell-cycle replication and nuclear targeting sequences (from EBNA-1 gene (Calos at Stanford, with Megabios); SV40 early promoter/enhancer or peptide sequences attached to the DNA).
Targeting systems based on cell receptor recognition by ligand linked to DNA have been described by Michael, S. I. and Curiel, D. T., Gene Therapy, 1994, 1: 223-232. Using the ligand recognized by such a receptor the DNA becomes selectively bound and internalized into the target cell (Wu, G. Y. and Wu, C. H., J. Biol. Chem., 1987, 262: 4429-4432). Poly-L-lysine (PLL), a polycation, has been used to couple a variety of protein ligands to DNA by chemical cross-linking methods. DNA is electrostatically bound to PLL-ligand molecules. Targetting systems have been published by Zenke et al., Proc. Nat. Acad. Sci. U.S.A., 1990, 87: 3655-3659 using transferrin receptor; Wu, G. Y. and Wu, C. H., J. Biol. Chem., 1987. 262: 4429-4432 using the asialoorosomucoid receptor, and Batra et al., Gene Therapy, 1994, 1: 255-260, using cell surface carbohydrates. Agents such as chloroquine or co-localised adenovirus can be used to reduce DNA degradation in the lysosomes (see Fisher, K. J. and Wilson, J. M., Biochem. J., 1994, 299, 49-58). Cristiano et al., Proc. Natl. Acad. Sci. U.S.A., 1993, 90: 11548-11552 has constructed adenovirus-DNA-ligand complexes. Patent references on receptor mediated endocytosis are: WO 92/05250 (asialoglycoproteins, University of Connecticut) and U.S. Pat. No. 5,354,844 (transferrin receptor, Boehringer).
DNA and ligand can be coated over the surface of the adenovirus to create a coated adenovirus (Fisher, K. J. and Wilson, J. M., Biochem. J., 1994, 299, 49-58). However the presence of two receptor pathways for DNA entry (ligand receptor and adenovirus receptor) reduces the specificity of this delivery system but the adenovirus receptor pathway can be eliminated by using an antibody against adenovirus fiber protein as the means for linkage to DNA (Michael, S. I. and Curiel, D. T., Gene Therapy, 1994, 1: 223-232). Use of purified endosomalytic proteins rather than intact adenovirus particles is another option (Seth, P., J. Virol., 1994, 68: 1204-1206).
The expression of a gene construct of the invention at its target site is preferably under the control of a transcriptional regulatory sequence (TRS). A TRS is a promoter optionally combined with an enhancer and/or an control element such as a genetic switch described below.
One example of a TRS is a xe2x80x9cgenetic switchxe2x80x9d that may be employed to control expression of a gene construct of the invention once it has been delivered to a target cell. Control of gene expression in higher eucaryotic cells by procaryotic regulatory elements (which are preferred for the present invention) has been reviewed by Gossen et al in TIBS, Dec. 18, 1993, 471-475. Suitable systems include the E. coli lac operon and the especially preferred E. coli tetracycline resistance operon. References on the tetracycline system include Gossen et al (1995) Science 268, 1766; Damke et al (1995) Methods in Enzymology 257, Academic Press; Yin et al (1996) Anal. Biochem. 235, 195 and; U.S. Pat. Nos. 5,464,758, 5,589,362, WO 96/01313 and WO 94/29442 (Bujard). An ecdysone based switch (International Patent Appln No.PCT/GB96/01195, Publication No. WO 96/37609, Zeneca) is another option. Other options are listed below. Connaught Laboratories (WO-93/20218) describe a synthetic inducible eukaryotic promoter comprising at least two different classes of inducible elements. Rhone-Poulenc Rorer (WO 96/30512) describe a tetracycline-related application for a conditional gene expression system. Ariad (WO 94/18317) describes a protein dimerisation based system for which in vivo activity has been shown. Bert O""Malley of the Baylor College of Medicine (WO 93/23431, U.S. Pat. No. 5,364,791, WO 97/10337) describes a molecular switch based on the use of a modified steroid receptor. The Whitehead Institute have an NF-KB inducible gene expression system (WO 88/05083). Batelle Memorial have described a stress inducible promoter (European patent EP 263908).
Examples of TRSs which are independent of cell type include the following: cytomegalovirus promoter/enhancer, SV40 promoter/enhancer and retroviral long terminal repeat promoter/enhancer. Examples of TRSs which are dependent on cell type (to give an additional degree of targeting) include the following promoters: carcinoembryonic antigen (CEA) for targeting colorectal, lung and breast; alpha-foetoprotein (AFP) for targeting transformed hepatocytes; tyrosine hydroxylase, choline acetyl transferase or neurone specific enolase for targeting neuroblastomas; insulin for targeting pancreas and; glial fibro acidic protein for targeting glioblastomas. Some oncogenes may also be used which are selectively expressed in some tumours e.g. HER-2/neu or c-erbB2 in breast and N-myc in neuroblastoma.
Accordingly, a preferred gene construct for use as a medicament is a construct comprising a transcriptional regulatory sequence which comprises a promoter and a control element which is a genetic switch to control expression of the gene construct. A preferred genetic switch control element is regulated by presence of tetracycline or ecdysone. A preferred promoter is dependent on cell type and is selected from the following promoters: carcinoembryonic antigen (CEA); alpha-foetoprotein (AFP); tyrosine hydroxylase; choline acetyl transferase; neurone specific enolase; insulin; glial fibro acidic protein; HER-2/neu; c-erbB2; and N-myc. Preferably the gene construct for use as a medicament described herein is packaged within an adenovirus for delivery to the mammalian host. A general review of targeted gene therapy is given in Douglas et al., Tumor Targeting, 1995, 1: 67-84.
The antibody encoded by the gene construct of the invention may be any form of antibody construct such as for example F(abxe2x80x2)2; F(abxe2x80x2), Fab, Fv, single chain Fv and V-min. Any suitable antibody construct is contemplated, for example a recently described antibody fragment is xe2x80x9cL-F(ab)2xe2x80x9d as described by Zapata (1995) in Protein Engineering, 8, 1057-1062. Disulphide bonded Fvs are also contemplated. For constructs based on CPG2 enzyme, Fab fragment constructs dimerised through enzyme dimerisation are preferred. Non-human antibodies may be humanised for use in humans to reduce host immune responses. A humanized antibody, related fragment or antibody binding structure is a polypeptide composed largely of a structural framework of human derived immunoglobulin sequences supporting non human derived amino acid sequences in and around the antigen binding site (complementarity determining regions or CDRs). Appropriate methodology has been described for example in detail in WO 91/09967, EP 0328404 and Queen et al. Proc Natl Acad Sci 86 10029, Mountain and Adair (1989) Biotechnology and Genetic Engineering Reviews 10, 1 (1992) although alternative methods of humanisation are also contemplated such as antibody veneering of surface residues (EP 519596, Merck/NIH, Padlan et al).
According to another aspect of the present invention there is provided a matched two component system designed for use in a mammalian host in which the components comprise:
(i) a first component that comprises a gene construct encoding a cell targeting antibody and a heterologous prodrug activating enzyme wherein the gene construct is capable of expressing the antibody and enzyme as a conjugate within a target cell in the mammalian host and wherein the conjugate can leave the cell thereafter for selective localisation at a cell surface antigen recognised by the antibody and;
(ii) a second component that comprises a prodrug which can be converted into an active drug by the enzyme.
Antibody directed enzyme prodrug therapy (ADEPT) is a known cancer therapeutic approach. ADEPT uses a tumour selective antibody conjugated to an enzyme. The conjugate is administered to the patient (usually intravenously), allowed to localise at the tumour site(s) and clear from the blood and other normal tissues. A prodrug is then administered to the patient which is converted by the enzyme (localised at the tumour site) into a cytotoxic drug which kills the tumour cells.
The present invention can be applied to any ADEPT system. Suitable examples of ADEPT systems include those based on any of the following enzymes: carboxypeptidase G2; carboxypeptidase A; aminopeptidase; alkaline phosphatase; glycosidases; xcex2-glucuronidase; penicillin amidase; xcex2-lactamase; cytosine deaminase; nitroreductase; or mutant host enzymes including carboxypeptidase A, carboxypeptidase B, and ribonuclease. Suitable references on ADEPT systems include Melton R G (1996) in J. National Cancer Institute 88, 1; Niculescu-Duvaz I (1995) in Current Medicinal Chemistry 2, 687; Knox R J (1995) in Clin. Immunother. 3, 136; WO 88/07378 (CRCT); Blakey et al., Cancer Res. 56, 3287-92, 1996; U.S. Pat. No. 5,587,161 (CRCT and Zeneca); WO 97/07769 (Zeneca); and WO 95/13095 (Wellcome). The heterologous enzyme may be in the form of a catalytic antibody; see for example EP 745673 (Zeneca). A review articles on ADEPT systems include Hay and Denny (1996), Drugs of the Future, 21(9), 917-931 and Blakey (1997), Exp. Opin. Ther. Patents, 7(9), 965-977.
A preferred matched two component system is one in which: the first component comprises a gene encoding the heterologous enzyme CPG2; and the second component prodrug is selected from N-(4-[N,N-bis(2-iodoethyl)amino]-phenoxycarbonyl)-L-glutamic acid, N-(4-[N,N-bis(2-chloroethyl)amino]-phenoxycarbonyl)-L-glutamic-gamma-(3,5-dicarboxy)anilide or N-(4-[N,N-bis(2-chloroethyl)amino]-phenoxycarbonyl)-L-glutamic acid or a pharmaceutically acceptable salt thereof. Preferred prodrugs for use with CPG2 are described in the following US patents from Zeneca Limited and Cancer Research Campaign Technology Limited: U.S. Pat. Nos. 5,714,148, 5,405,990, 5,587,161 and 5,660,829.
In another aspect of the invention there is provided a method for the delivery of a cytotoxic drug to a site which comprises administering to a host a first component that comprises a gene construct as defined herein; followed by administration to the host of a second component that comprises a prodrug which can be converted into a cytotoxic drug by the heterologous enzyme encoded by the first component. A preferred method for delivery of a cytotoxic drug to a site is one in which the first component comprises a gene encoding the heterologous enzyme CPG2; and the second component prodrug is selected from N-(4-[N,N-bis(2-iodoethyl)amino]phenoxycarbonyl)-L-glutamic acid, N-(4-[N,N-bis(2-chloroethyl)amino]-phenoxycarbonyl)-L-glutamic-gamma-(3,5-dicarboxy)anilide or N-(4-[N,N-bis(2-chloroethyl)amino]-phenoxycarbonyl)-L-glutamic acid or a pharmaceutically acceptable salt thereof.
Abbreviations used herein include:
In this specification conservative amino acid analogues of specific amino acid sequences are contemplated which retain the relevant biological properties of the component of the invention but differ in sequence by one or more conservative amino acid substitutions, deletions or additions. However the specifically listed amino acid sequences are preferred. Typical conservative amino acid substitutions are tabulated below.
Amino acid nomenclature is set out below.
In this specification nucleic acid variations (deletions, substitutions and additions) of specific nucleic acid sequences are contemplated which retain which the ability to hybridise under stringent conditions to the specific sequence in question. Stringent conditions are defined as 6xc3x97SSC, 0.1% SDS at 60xc2x0 for 5 minutes. However specifically listed nucleic acid sequences are preferred. It is contemplated that chemical analogues of natural nucleic acid structures such as xe2x80x9cpeptide nucleic acidxe2x80x9d (PNA) may be an acceptable equivalent, particularly for purposes that do not require translation into protein (Wittung (1994) Nature 368, 561).
The invention will now be illustrated by reference to the following non-limiting Examples. Temperatures are in degrees Celsius.